The present invention relates to an electric power steering device equipped with an anti-theft function and a method for manufacturing same.
A conventional electric power steering device 101 equipped with an anti-theft function, which is illustrated in FIG. 6, comprises sensor housing 102 and a steering shaft 103 having a part which is surrounded by this sensor housing 102. A lock member (omitted from the drawings), which is supported by a member fixed to the vehicle body side, is received by a receiving portion 104 provided on the outer circumference of the steering shaft 103 on the exterior of the sensor housing 102. Thereby, the rotation of the steering shaft 103 is restricted to provide an anti-theft function. In this conventional example, a tubular member 109 is integrated with the steering shaft 103 on its outer circumference by press fitting, and the receiving portion 104 is constituted by the inner surface of a recessed portion formed on the tubular member. A torque sensor 105 having a magnetic flux generating coil 108, which is provided so as to surround the steering shaft 103, is provided within the sensor housing 102. This torque sensor 105 has input and output shafts 111, 112 which constitute the steering shaft 103, and which are mutually connected so as to be capable of elastic relative rotation. The torque which is transmitted by the steering shaft 103 is detected on the basis of changes in the relative position in the circumferential direction of a first magnetic flux transmitting member 115 which is attached to the input shaft 111 and a second magnetic flux transmitting member 116 which is attached to the output shaft 112. A driving gear 107 which meshes with a driven gear 106 provided on the outer circumference of the output shaft 112 is driven by an electric actuator (omitted from the drawings), and the auxiliary steering power generated by this electric actuator is transmitted to the steering shaft 103. The coil 108 is disposed in a position between the receiving portion 104 and the driven gear 106, in which the generated magnetic flux is transmitted through the two magnetic flux transmitting members 115, 116. The outer diameter D1 of the receiving portion 104 is made smaller than the inner diameter D3 of the coil 108, and the outer diameter D2 of the driven gear 106 is made larger than the inner diameter D3 of the coil 108. The steering shaft 103 has an upper shaft 113 which is a separate entity to the input and output shafts 111, 112, and the receiving portion 104 is provided on the outer circumference of this upper shaft 113. The upper shaft 113 is connected via a pin 120 to the input shaft 3 so as to be capable of rotation in accompaniment therewith. Further, a tubular column 119 is provided surrounding the upper shaft 113 and disposed in a position which is unchanging with respect to the sensor housing 102.
Conventionally, when manufacturing the aforementioned electric power steering device 101, the input and output shafts 111, 112, the upper shaft 113, the magnetic flux transmitting members 115 and 116, and the driven gear 106 are formed into an assembly, and this assembly is inserted into the sensor housing 102. Since the outer diameter D2 of the driven gear 106 is larger than the inner diameter D3 of the coil 108, the driven gear 106 cannot be passed through the coil 108. Therefore, the assembly is inserted into the sensor housing 102 from the upper shaft 113 side.
When the aforementioned electric power steering device 101 is used in a vehicle in which the outer diameter of the steering shaft 103 is large, the outer diameter D1 of the receiving portion 104 provided on the outer circumference of the steering shaft 103 also becomes large. Moreover, when the receiving portion 104 is mounted onto the steering shaft 103 via a torque limiter, which prevents excessive torque from acting upon the steering wheel, so as to improve the anti-theft function by preventing damage of the receiving portion 104 or the lock member, the outer diameter D1 of the receiving portion 104 becomes even larger. Hence, the outer diameter D1 of the receiving portion 104 becomes larger than the inner diameter D3 of the coil 108. As a result, not only the driven gear 106, but also the receiving portion 104 is unable to pass through the coil 108, and therefore the assembly formed from the input and output shafts 111, 112, the upper shaft 113, the magnetic flux transmitting members 115 and 116, and the driven gear 106 cannot be inserted into the sensor housing 102. Consequently, enlarging the inner diameter D3 of the coil 108 has been considered. However, when the inner diameter D3 of the coil 108 becomes larger, the entire device is increased in size, and problems arise in that the mounting of the steering device on the vehicle becomes difficult and costs increase.
An object of the present invention is to provide an electric power steering device equipped with an anti-theft function and a method for manufacturing same which can solve the aforementioned problems.
The electric power steering device equipped with an anti-theft function according to the present invention comprises a sensor housing, a steering shaft having a part which is surrounded by this sensor housing, and a torque sensor having a magnetic flux generating coil which is provided within the sensor housing so as to surround the steering shaft. This torque sensor has input and output shafts which constitute the steering shaft, and which are mutually connected so as to be capable of elastic relative rotation. The torque that is transmitted by the steering shaft is detected on the basis of changes in the output of the coil in response to changes in the relative position in the circumferential direction of a first magnetic flux transmitting member which is attached to the input shaft and a second magnetic flux transmitting member which is attached to the output shaft. An auxiliary steering power transmitting driven gear is provided on the outer circumference of the output shaft. The steering shaft has an upper shaft which is provided as a separate entity to the input and output shafts. A receiving portion is provided on the outer circumference of this upper shaft, and the coil is disposed in a position between the receiving portion and the auxiliary steering power transmitting driven gear in which the generated magnetic flux is transmitted through the two magnetic flux transmitting members. A lock member which is supported by a member fixed to the vehicle body side is received by the receiving portion, whereby the rotation of the steering shaft is restricted.
The manufacturing method of the present invention is characterized in that, upon manufacture of the electric power steering device equipped with an anti-theft function, the outer diameter of the receiving portion and the outer diameter of the auxiliary steering power transmitting driven gear are made to be larger than the inner diameter of the coil, and the sensor housing, coil, mutually connected input and output shafts, the two magnetic flux transmitting members and the driven gear are formed into an assembly, whereupon the upper shaft with the receiving portion provided on its outer circumference is connected to the input shaft so as to be capable of rotation in accompaniment therewith.
According to this method of the present invention, the outer diameter of the receiving portion and the outer diameter of the auxiliary steering power transmitting driven gear are made to be larger than the inner diameter of the coil, and hence this method can respond to such cases as when the receiving portion is provided on the outer circumference of a steering shaft with a large outer diameter, or when the receiving portion is mounted onto the steering shaft via a torque limiter in order to improve the anti-theft function. In this case, the sensor housing, coil, input shaft, output shaft, the two magnetic flux transmitting members, and the driven gear are formed into an assembly, whereupon the upper shaft with the receiving portion provided on its outer circumference is connected to the input shaft so as to rotate in accompaniment therewith. Hence, even though both the driven gear and the receiving portion cannot pass through the coil, assembling can be performed without enlarging the inner diameter of the coil.
It is preferable that the two magnetic flux transmitting members are relatively disposed in a given position, whereupon the input shaft and output shaft are connected to each other, and the upper shaft is connected to the input shaft so as to be capable of relative displacement in the axial direction.
In the torque sensor, which detects the torque that is transmitted by the steering shaft on the basis of changes in the output of the coil in response to changes in the relative position in the circumferential direction of the first magnetic flux transmitting member and second magnetic flux transmitting member, a detection reference value to detect torque is the output of the coil when torque is zero. The absolute value of this detection reference value varies in accordance with the relative position in the axial direction of the first magnetic flux transmitting member and second magnetic flux transmitting member. Thus, by adjusting the relative position in the axial direction of the input shaft to which the first magnetic flux transmitting member is attached and the output shaft to which the second magnetic flux transmitting member is attached, the relative position in the axial direction of the two magnetic flux transmitting members is adjusted such that the output of the coil when torque is zero becomes the detection reference value. By connecting the input shaft and output shaft to each other following this adjustment, the two magnetic flux transmitting members can be relatively disposed in a given position in which the coil output becomes the reference value. If excessive force acts upon the connecting portion between the input shaft and the output shaft, the relative disposition of the two magnetic flux transmitting members fluctuates, whereby the torque detection accuracy deteriorates. Thus, by making the upper shaft capable of displacement in the axial direction relative to the input shaft, excessive force can be prevented from acting upon the connecting portion of the input and output shafts. Excessive force can also be prevented from acting upon the connecting portion of the input and output shafts when a column, which surrounds the upper shaft and which is disposed in an unchanging position with respect to the sensor housing, is connected to the upper shaft so as to be capable of accompanying displacement in the axial direction.
The electric power steering device equipped with an anti-theft function of the present invention is characterized in that the outer diameter of the receiving portion and the outer diameter of the auxiliary steering power transmitting driven gear are made to be larger than the inner diameter of the coil, and the upper shaft is connected to the input shaft so as to be capable of accompanying rotation and relative displacement in the axial direction.
The electric power steering device equipped with an anti-theft function of the present invention can be manufactured according to the method of the present invention.
According to the present invention, an improvement in the mounting characteristic to the vehicle, a reduction in costs, and an improvement in the anti-theft function can be effected without enlarging the coil of the torque sensor which detects steering torque, and further, an electric power steering device equipped with an anti-theft function, which is capable of preventing a deterioration in the torque detection accuracy, and a method of manufacturing same can be provided.